Method of miscible flooding



SEARCH FEW? Feb. 23, 1965 J. N. DEW ETAL 3,170,513

METHOD OF MISCIBLE FLOODING Filed Sept. 26, 1960 .F I8 20 |o I Is FIG. I

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INVENTORS JOHN M 05w By PHILIP w REED ZMW ATTORNEY United States Patent 3,170,513 METHOD OF MISClIBLE FLOODING John N. Dew and Philip W. Reed, Ponca City, Okla., assignors to Continental Oil Company, Ponca City, Okla., a corporation of Delaware Filed Sept. 26, 1960, Ser. No. 58,236 5 Claims. (Cl. 166-9) The present invention pertains to the recovery of hydrocarbons from subterranean reservoirs by the utilization of miscible fluid flooding media. More particularly this invention relates to the secondary recovery of hydrocarbons by a method of combined flooding media which is novel and unique in the art, in order that substantially all of the oil in a reservoir may be recovered.

The secondary recovery of hydrocarbons generally refers to those recovery efforts which are applied in order to obtain production subsequent to the economic production obtainable by utilizing naturally-occurring energy or conventional pumping means. The use of miscible fluids in secondary recovery operations is known in the art, particularly the injection of low molecular weight normally gaseous hydrocarbons. Methods utilizing such hydrocarbons are exteremely successful with regard to the displacement efliciency of the hydrocarbons, particularly the ability to displace essentially all of the hydocarbons from the formation; but the volumetric efliciency of this flooding media is a disadvantage. The hydrocarbons inherently finger and channel to a great extent, and a large portion of the reservoir is bypassed, though the volume of inejcted hydrocarbons may be great, which brings up the further disadvantage of expense per volume and inability to obtain suflicient volumes of the flooding medium. In order to overcome these disadvantages, the low molecular weight normally gaseous hydrocarbons, hereinafter referred to as L.P.G., have been utilized in combination with other known flooding media such as water and gas. The use of a zone of the displacement hydrocarbon between oil and displacing gas in reservoirs of suitable pressure and temperature as determined from the phase behavior of the hydrocarbons present is well known in the art, as is the simultaneous addition of water with the displacement hydrocarbon and the gas to reduce the mobility of these low viscosity hydrocarbons. The combination of injecting LPG. and water can eliminate most of the channelling and fingering of a completely miscible flooding system, making recovery more economical.

placement hydrocarbon through the oil-bearing formation,

thereby displacing the reservoir oil to recovery wells. Injection of the displacement hydrocarbon together with water is done in such volume that a sufficient amount is placed in the reservoir to permit a miscible displacement of the reservoir oil by the displacement hydrocarbon and miscible displacement thereof by the gas. This invention is directed to a method of recovery based upon the relation of the displacement hydrocarbon and the water injected in combination providing water movement at a velocity greater than the velocity of the displacement hydrocarbon, and the relation of the gas and the water injected in combination, providing gas movement at a velocity greater than the velocity of the Water. An object of this invention is to provide an economical method of secondary recovery of at least 90 percent of the hydrocarbons originally in place within a reservoir.

Another object of this invention is to provide a method of secondary recovery wherein the amount of displacement hydrocarbon needed is maintained at a minimum,

3,170,513 Patented Feb. 23, 1965 while retaining the advantages of completely miscible flooding operation within the hydrocarbon phase.

A further object of this invention is to provide a method of miscible secondary recovery which can be applied with greater speed in a field situation to enable more rapid economic returns.

A still further object of this invention is to provide a method of miscible secondary recovery which overcomes and avoids the disadvantages of the prior art.

Other objects and advantages of the present invention will become apparent from the following detailed description of the invention taken in conjunction with the accompanying drawings, in which:

FIGURE 1 represents the reservoir displacements during the initial recovery phase of the invention during the injection of the liquefied low molecular weight hydrocarbon and water.

FIGURE 2 represents the reservoir displacements during an early recovery phase subsequent to the commencement of gas and water injection.

FIGURE 3 represents the reservoir displacements during an intermediate recovery phase subsequent to the injection of substantial amounts of gas and water.

FIGURE 4 represents the reservoir displacements during the L.P.G. recovery phase subsequent to the recovery of the reservoir hydrocarbons.

The liquefied low molecular weight hydrocarbon, here-- inafter referred to as the displacement hydrocarbon, used for secondary recovery is normally obtained from field gas processing plants, the volumes produced being inherently limited in comparison to oil production. In order to preserve the reservoir pressure to prevent loss of conditions of miscibility, it is frequently necessary to inject amounts of materials equal to the volume of hydrocarbons produced from the reservoir, but the unavailability of the displacement hydrocarbon makes it impossible to conduct an economical miscible flood project. Obtaining the volume necessary for a conventional field project requires an extended period of time; in general, from months for a small project having displacement hydrocarbon available from a large production field, to several years for a large project having such available from a production field only a few times larger than the project area. The method of this invention uses large volumes of water with the displacement hydrocarbon, and water and gas, so that the volume of material injected is large compared to that possible with the injection of displacement hydrocarbon only. Since water and gas are normally available in large quantities and low cost, a project can be conducted at rates promoting eflicient displacement within the reservoir.

The method of the present invention is adaptable to application to any hydrocarbon-bearing reservoir, but most readily on a field-wide basis, wherein the reservoir is traversed by several well bores. The wells may be afranged in a conventional manner, such as a five-spot or line pattern, or as the individual situation demands, with certain of the Wells being used for the injection of the displacement media and others for recovery of the hydrocarbons.

Prior to the application of this method to a reservoir it is necessary to have certain data on the reservoir which is readily determinable by procedures known in the art, such as effective floodable pore volume of the formation, average interstitial Water saturation, applicable relative permeability characteristics, and amount of displacement hydrocarbon required to maintain miscibility between the reservoir oil and displacing gas during the life of the flood. Thereafter the relative velocities of the water and the displacement hydrocarbon, and the water and gas, can be determined by trial saturations to define saturations giving the desired velocity ratios from which the required volumes of displacement hydrocarbon, gas and water are determined. The pressure Within the reservoir should be in excess of the vapor pressures of the liquefied hydrocarbon injected therein, which may occur naturally or may be established by injecting air, gas or other material to raise the pressure in a conventional manner.

The initial recovery step of the present invention is the injection of a liquefied low molecular weight hydrocarbon containing 2 to 7 carbon atoms and water into the reservoir through at least one injection well. This liquefied hydrocarbon can be a single hydrocarbon or a mixture of those in the range specified. This invention may be accomplished by simultaneously introducing the displacement hydrocarbon and water, or it has been found that a slugwise injection of incremental amounts of the water and displacement hydrocarbon has the same effect; therefore the hydrocarbon can be injected in amounts of 30 to 200 barrels per foot of formation exposed in the injection well, followed by a similar injection of water. Upon injection into the reservoir for a small distance, in the order of approximately 10 to 50 feet, depending on the amounts of each injected, the displacement hydrocarbon and water become sufficiently mixed to have the same effect as simultaneous injection while utilizing less equipment.

Referring to FIGURE 1 of the drawings, a subterranean hydrocarbon-bearing formation 10 is traversed by an injection well 12 and a recovery well 14. The injection of material through well 12 during the initial step into formation 10 results in an oil-bearing segment 16, and a displacement hydrocarbon and water containing segment 18, wherein the materials are commingled uniformly regardless of the manner of injection. There is also a distinct segment which is predominantly a water segment 20, caused by the greater velocity of the water injected with the displacement hydrocarbon.

The particles of a subterranean reservoir are normally water wet, due to the presence of connate water inherently present, together with the reservoir hydrocarbons. The total injected hydrocarbon necessary to maintain miscible displacement within the reservoir should be an amount from about 3 to about 15 percent, preferably 5 percent, of the hydrocarbon-filled pore space of the reservoir, as readily determinable by means known in the art. The mixture of displacement hydrocarbon and water moves through the reservoir in the same areas without appreciable gravity separation due to the fact that the injection hydrocarbon moves through the interior of the channels between the particles to displace the hydrocarbons, and the Water moves through the remainder of the channels and adjacent the connate Water. Therefore the injected hydrocarbon provides displacement efficiency, and the water provides volumetric efficiency. Movement of a fluid through porous media is related to the saturation or proportion of the fluid present due to the inherent efforts of the relative permeabilities of the reservoir. The velocity of movement of water or a hydrocarbon is calculated at any given saturation from the relative permeability at that saturation, the fluid viscosity, and the saturation change from the previous condition to the saturation under consideration. In the mixture of displacement hydrocarbon and water injected, the proportion of water is such that the velocity of movement of water is in excess of the velocity of L.P.G. by at least 5 percent, and preferably in the order of 30 to 50 percent, thereby allowing larger volumes of water to be utilized during the injection of the hydrocarbon volume required for eflicient miscibility.

The second step of the present invention is the injection of a mixture of water and hydrocarbon gas, such as methane or inert gas, such as carbon dioxide, combustion gas or nitrogen, injected in a simultaneous or slugwise manner as described in the foregoing initial phase. The water will move through the reservoir essentially in. the previously-established channels wherein the initially-injected water exists, and the gas will move through those channels wherein displacement hydrocarbon is present. The avoidance of fingering or adverse channelling established in the initial phase is maintained, thereby allowing continuance of the high volumetric efficiency. Conversely, due to the initial phase, the gas is injected in amounts such that it will travel faster than the water injected in association therewith enabling the injected gas to flow through the water injected in both phases of the method and contact the injected hydrocarbon in such a manner as to increase the velocity thereof. This increase in velocity causes the displacement hydrocarbon to advance through the water injected in combination therewith, and the continued injection of gas advances the injected hydrocarbon ahead of the water.

Referring to FIGURE 2 of the drawing, the injection of gas and water through well 12 of the second step creates a gas and water containing segment 22 within formation 10 and the greater velocity of the gas causes the displacement hydrocarbon of the initial phase to be displaced to effectively overtake the water segment 20 and replace it by enlarging segment 18. The volume of gas should be sufficient to establish a gas velocity at least 10 percent, and preferably in the order of 50 to 75 percent, greater than that of the water. As the injection of gas and water are continued, FIGURE 3 reflects the displacement of the various components within the reservoir. The gas from segment 22 maintaining the greater velocity than the water therein proceeds ahead in the reservoir forming a gas segment 24 causing the displacement hydrocarbon of segment 18 to be displaced at an increased velocity as indicated by a displacement hydrocarbon segment 26. As the injections are made into formation 10, the oilbearing segment 16 is reduced in size as the oil is produced through well 14 to the surface.

The ultimate step of the present invention is the con tinued injection of amounts of gas together with Water in such a manner as to displace all of the previously-injected hydrocarbon into the recovery well before water enters the well in order that the displacement hydrocarbon can be produced and not abandoned within the reservoir. This also avoids the production of water from Within the reservoir, thereby retaining it as a filler to be utilized in applying the present method to adjacent reservoirs. Referring to FIGURE 4 of the drawing, the effect of the continued injection of gas and water through well 12 into formation 10 causes substantially all of the oil to be recovered at well 14 as evidenced by the lack of a segment 16 in this figure. The water originally injected in zone 18 is bypassed by the gas due to the velocity differential and substantially all of the displacement hydrocarbon formerly within segments 18 and 26 is displaced due to the expansion of segment 24 as represented in FIGURE 3. As shown in the figures, the continuous gas and water injection causes the oil segment 16 to be swept clean of oil and displacement hydrocarbon injected in segment 18 is recovered while a substantial amount of the gas injected during the second phase can be recovered also by lowering the pressure about the recovery well 14.

p The mechanics of the present method are readily determinable by known calculations within the art. These mechanics should be adjusted for the individual reservoir in order that the individual phases may be so scheduled as to provide a definite break through of the displacement hydrocarbon ahead of the initial water zone at some point previously determined to be desirable in order to obtain maximum recovery. In order to more fully disclose and teach the invention, the following example is included by way of illustration.

Example A conventional five-spot well pattern covering 40 acres and located in the North Meadow Creek field in Johnson County, Wyoming, traversed the oil-bearing Lakota sand formation at a depth 'of approximately 7,320 feet. The method of secondary recovery of the present invention could be applied to the portion of the reservoir encompassed within the area of the pattern most readily by utilizing the center well as the injection well and the remaining four peripheral wells at an average distance of about 860 feet as recovery wells. The formation sand having a thickness of feet has an average porosity of 14 percent, an average permeability of 110 md., and saturations as follows: interstitial water of 23.6 percent, reservoir oil of 57.3 percent, and reservoir gas of 19.1 percent.

Determinations by known methods based on the foregoing data indicate the overall volume of the formation would be 1,584,000 cubic feet, and the pore volume would be 39,400 barrels and containing approximately 22,600 barrels of reservoir oil which is subject to recovery by the present method. The amount of liquefied low molecular weight hydrocarbon necessary to effect recovery would be 4 percent of the pore space; so 1,575 barrels of propane are simultaneously injected together with 8,033 barrels of water through the injection well in order to cause the water to move at the necessary velocity higher than the L.P.G. velocity.

After the L.P.G. and water injection of the first phase of the invention, a volume of 13,240 barrels of water and 3,220,000 cubic feet of essentially methane gas would be simultaneously injected into the formation through the injection well. The injection of excess methane moves a portion of it through the formation ahead of the simultaneously injected water at increased velocity whereby it contacts and displaces the previously injected L.P.G. The methane displaces the L.P.G. through the water simultaneously injected therewith.

Essentially all of the injected L.P.G. is used to displace the remaining reservoir oil into the recovery wells and the L.P.G. is continually displaced until it is recovered from the formation. The recovery efforts in such a field situation would be such as to effect the production of 18,100 barrels of the reservoir oil in place at the outset or 80 percent, and 1,100 barrels of the injected L.P.G. or 70 percent.

It will be understood that the example included herein is illustrative only and that the invention is to be taken as limited only by the scope of the appended claims.

We claim:

1. A method for the recovery of hydrocarbons from a subterranean hydrocarbon-bearing reservoir traversed by an injection well and a recover well which comprises:

(a) injecting a fimfied low molecular weight hydrocarbon and water into said reservoir, said hydrocarbon being in an amount from about 3 to 15 percent of the reservoir hydrocarbon pore space and said water being in an amount for a displacement velocity in said reservoir greater than the hydrocarbon of said first mixture;

(b) injecting a second mixture of water and hydrocarbon gas, said gas being in an amount for a displacement velocity in said reservoir greater than the water of said second mixture;

(0) controlliugllhe velocity of the gasgfsaid second hnixturedisplacingrsaid first mixture in such a manner for displacement of the hydrocarbon of said first mixture through and ahead of the water of said first (a!) recovering hydrocarbons from said reservoir via said recovery well.

2. A method as set forth in claim 1 wherein the low molecular weight hydrocarbon and water components are injected in incremental slugs forming said first mixture in the reservoir adjacent said first well.

3. A method as set forth in claim 1 wherein the water and hydrocarbon gas components are injected in incremental slugs forming said second mixture in the reservoir adjacent said first well.

4. A method for the recovery of hydrocarbons from a subterranean hydrocarbon-bearing reservoir traversed by an injection well and a recovery well which comprises:

(a) injecting a first mixture of liquefied low molecular weight hydrocarbon and water into said reservoir, said hydrocarbon being in an amount from about 3 to 15 percent of the reservoir hydrocarbon pore space and said water being in an amount for a displacement velocity in said reservoir at least 5 percent greater than the hydrocarbon of said first mixture;

(b) injecting a second mixture of water and hydrocarbon gas, said gas being in an amount for a displacement velocity in said reservoir at least 10 percent greater than the water of said second mixture;

(c) controlling the velocity of the gas of said second mixture displacing said first mixture in such a manner for displacement of the hydrocarbon of said first mixture through and ahead of the water of said first mixture prior to reaching said recovery well; and

(d) recovering hydrocarbons from said reservoir via said recovery well.

5. A method for the recovery of hydrocarbons from a subterranean hydrocarbon-bearing reservoir traversed by an injection well and a recovery well which comprises:

(a) injecting a first mixture of liquefied low molecular weight hydrocarbon and water into said reservoir, said hydrocarbon being in an amount of about 5 percent of the reservoir hydrocarbon pore space and said water being in an amount for a displacement velocity in said reservoir from about 30 to 50 percent greater than the hydrocarbon of said first mixture;

(b) injecting a second mixture of water and hydrocarbon gas, said gas being in an amount for a displacement velocity in said reservoir from about 50 to 75 percent greater than the water of said second mixture;

(0) controlling the velocity of the gas of said second mixture displacing said first mixture in such a manner for displacement of the hydrocarbon of said first mixture through and ahead of the water of said first mixture prior to reaching said recovery well; and

(d) recovering hydrocarbons from said reservoir via said recovery well.

References Cited in the file of this patent UNITED STATES PATENTS 2,669,307 Mulholland et al Feb. 16, 1954 3,096,821 Dyes July 9, 1963 FOREIGN PATENTS 696,524 Great Britain Sept. 2, 1953 OTHER REFERENCES What is Miscible Displacement, The Petroleum Enmixture prior to reaching said recovery well; and gineer, August 1959, Kieschnick. 

1. A METHOD FOR THE RECOVERY OF HYDROCARBONS FROM A SUBTERRANEAN HYDROCARBON-BEARING RESERVOIR TRAVERSED BY AN INJECTION WELL AND A RECOVERY WELL WHICH COMPRISES: (A) INJECTING A FIRST MIXTURFE OF LIQUEFIED LOW MOLECULAR WEIGHT HYDROCARBON AND WATER INTO SAID RESERVOIR, SAID HYDROCARBON BEING IN AN AMOUNT FROM ABOUT 3 TO 15 PERCENT OF THE RESERVOIR HYDROCARBONS PORE SPACE AND SAID WATER BEING IN AN AMOUNT FOR A DISPLACEMENT VELOCITY IN SAID RESERVOIR GREATER THAN THE HYDROCARBON OF SAID FIRST MIXTURE; (B) INJECTING A SECOND MIXTURE OF WATER AND HYDROCARBON GAS, SAID GAS BEING IN AN AMOUNT FOR A DISPLACEMENT VELOCITY IN SAID RESERVOIR GREATER THAN THE WATER OF SAID SECOND MIXTURE; (C) CONTROLLING THE VELOCITY OF THE GAS OF SAID SECOND MIXTURE DISPLACING SAID FIRST MIXTURE IN SUCH A MANNER FOR DISPLACEMENT OF THE HYDROCARBON OF SAID FIRST MIXTURE THROUGH AND AHEAD OF THE WATER OF SAID FIRST MIXTURE PRIOR TO REACHING SAID RECOVERY WELL; AND (D) RECOVERING HYDROCARBONS FROM SAID RESERVOIR VIA SAID RECOVERY WELL. 